linux-kernel - Re: [PATCH v2 07/10] KVM: x86: Always populate L1 GPA for KVM_MAP

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Message-ID: <245f8011e1f8cccb16a25f080d9521376172f909.camel@intel.com>
Date: Mon, 15 Apr 2024 19:37:52 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>, "federico.parola@...ito.it"
	<federico.parola@...ito.it>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"michael.roth@....com" <michael.roth@....com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>
Subject: Re: [PATCH v2 07/10] KVM: x86: Always populate L1 GPA for
 KVM_MAP_MEMORY

On Wed, 2024-04-10 at 15:07 -0700, isaku.yamahata@...el.com wrote:
> @@ -5882,18 +5884,40 @@ int kvm_arch_vcpu_map_memory(struct kvm_vcpu *vcpu,
>         if (!tdp_enabled)
>                 return -EOPNOTSUPP;
>  
> +       /* Force to use L1 GPA despite of vcpu MMU mode. */
> +       is_smm = !!(vcpu->arch.hflags & HF_SMM_MASK);
> +       if (is_smm ||
> +           vcpu->arch.mmu != &vcpu->arch.root_mmu ||
> +           vcpu->arch.walk_mmu != &vcpu->arch.root_mmu) {
> +               vcpu->arch.hflags &= ~HF_SMM_MASK;
> +               mmu = vcpu->arch.mmu;
> +               walk_mmu = vcpu->arch.walk_mmu;
> +               vcpu->arch.mmu = &vcpu->arch.root_mmu;
> +               vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
> +               kvm_mmu_reset_context(vcpu);
> +       }
> +
>         /* reload is optimized for repeated call. */

After the kvm_mmu_reset_context(), what benefit is there to the operation? And
it happening for every call of kvm_arch_vcpu_map_memory()?

>         kvm_mmu_reload(vcpu);